The present invention relates to a fuel supply system for an internal-combustion engine, especially for supplying diesel to an endothermic diesel-cycle engine installed in a motor vehicle.
A system of the type described above generally comprises, in the prior art, a fuel supply tank (at low pressure) and a fuel distribution manifold (at high pressure), from which the fuel is fed into the engine through a plurality of injectors.
The fuel supply tank and the distribution manifold are connected to each other by a pumping unit in which a fluid line comprises a low-pressure portion and a high-pressure portion. These portions are connected by a high-pressure pump. The low-pressure portion comprises a pre-feed pump mounted in series with the high-pressure pump on the aforementioned fluid line.
The low-pressure portion also includes a plurality of low-pressure branches and a plurality of fluid-line components, each of which is connected to at least one low-pressure branch by a connector provided with a coupling inserted partly into the connector and partly into the low-pressure branch.
The couplings mentioned above are usually made of metal and are fixed inside their connectors by screwing or pressure; in this second case the couplings are usually made of brass.
A system such as that described above has the drawback that the metal couplings are heavy and, in the case of screw couplings, the couplings and their connectors require expensive machining by chip removal.
In the case of brass couplings there is the drawback that Zn and Cu ions from the coupling itself dissolve into the fuel causing both internal abrasion of the pumping unit and deposition, inside the injectors, of hard sediments, which reduce the flow rate and uniformity of the distribution of the fuel entering the engine.